A double diffused drain (DDD) may be used as a source and/or drain in a high voltage metal-oxide semiconductor (HVMOS) transistor to provide a high breakdown voltage and to prevent electrostatic discharge that may result in the destruction of a semiconductor device. Hot electron effects may be caused by shorted channel lengths in a MOS transistor. Using a DDD may also provide a solution to hot electron effects and prevent electrical breakdown in the source/drain under high voltage loading.
Many prior HVMOS transistors have a shallow junction depth for the DDD region. Such transistors having a shallow junction depth for the DDD region may provide a breakdown voltage of only about 22 volts, and thus may only be used reliably for a device with an operating voltage between about 12 volts and about 16 volts, for example. Yet, it would be desirable in many cases to provide an HVMOS transistor with a higher breakdown voltage and a higher limit on the operating voltage. Also, it would be desirable to provide such an HVMOS transistor while making little or no changes to a current process flow used in forming an HVMOS transistor while forming a low-voltage MOS transistor in parallel.